For many years, a need has existed for a method to continuously monitor the performance of critical components of heat recovery steam generators in order to improve their long-term efficiency and reliability. The present invention provides a new approach to the capture, analysis and use of infrared thermography data for the purpose of improving the operation and reliability of key components of HRSGs, thereby reducing the possibility of a catastrophic failure of such systems and increasing their overall efficiency.
Many processes associated with gas turbine engines, particularly HRSGs, control excess thermal energy generated during their operation (such as the heat of combustion) by using the energy as a heat source for other systems. However, simply identifying and controlling a heat source or thermal pattern is not enough to identify and predict potential equipment failures. In order to be fully effective, the system needs to be capable of monitoring and detecting temperature changes to key pieces of equipment and then comparing any detected operational changes over time to corresponding control models. Once a base line thermal signature is obtained and understood for a particular piece of equipment, deviations from the normal temperature signature can provide valuable information regarding a developing or existing problem.
As detailed below, it has been found that infrared thermal imaging can be used effectively to identify a problem in HRSG components and help limit or control the root cause of any overheating or potential failure. In many cases, the heat generated by a defective component may only be indirectly visible to an IR camera as the heat conducts through the component and appears as a thermal gradient on the object surface. A need therefore exists for an IR thermography system that can accurately correlate IR data in real time to specific HRSG components or locations within the HRSG that can be continuously monitored or controlled.
The invention also contemplates the possibility of using other test equipment, such as vibration analysis tools, chemical analysis or even ultrasound, in combination with IR thermographs generated by an IR camera to help pinpoint the exact location and nature of an operational problem. Once a thermal anomaly is detected, the combination of IR and other tools can help isolate, control or rectify the root cause of the problem. The use of infrared thermography for condition monitoring as outlined below can also be adapted to components that are not directly associated with an HRSG, including various gas turbine mechanical systems (e.g., compressors, motors, turbines, rotors and pumps), or even electrical components (e.g., transformers, relays, switches, transmission lines, bus connections, fuses and even circuit breakers). Currently, HRSG plant operators monitor the operation and condition of equipment only routinely, normally waiting until a unit is shut down, e.g., in intervals of three to six months up to a year. During those occasions, periodic recorded temperature differences on the surface of selected components can be used to assess equipment operation based on target design criteria. However, as noted above, such occasional, infrequent monitoring is far less effective in predicting or preventing a catastrophic failure of HRSG components or other critical gas turbine equipment.
In the exemplary embodiments of the invention described below, the following definitions apply to certain key terms:
“Thermal sensitivity”: The smallest change in IR radiation level that an IR camera is capable of recording (normally expressed in terms of a percentage of temperatures in degrees centigrade).
“Nominal temperature range”: A temperature measurement from −40° C. up to 2000° C. (the current operating range possible with most IR cameras).
“Environmental temperature”: The range of temperature at which the IR camera may be safely operated without suffering from process conditions that could adversely affect performance.
“Thermal resolution”: The smallest measurable difference in temperature between two related IR measurements over time.
“Spatial resolution”: A measure of the fineness of detail in the IR image which is directly proportional to the number of pixels representing the image.
“IR accuracy”: A measure of the difference between the true surface temperature and calculated temperature based on IR image data.
“Spot size ratio”: The maximum distance the IR camera can be positioned from a target location, taking into account the size of the target and acceptable temperature measurement accuracy.